Alternating current railway track circuits employing gas-filled electron tubes



Dec. 29, 1953 MARTIN 2,664,498

P. N. ALTERNATING CURRENT RAILWAY TRACK CIRCUITS EMPLOYING GAS-FILLED ELECTRON TUBES Original-Filed July 18, 1944 60126005 CL'Pcae'.

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PQZZZ iv: Mapaki BY Ah Lu k Patented Dec. 29, 1953 ALTERNATING CURRENT RAILWAY TRACK CIRCUITS EMPLOYING GAS-FILLED ELEC- TRON TUBES Paul N. Martin,

Penn Township, Allegheny County, Pa. assignor to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application April 30, 1946, Serial No. 665,944, which is a division of application Serial No. 545,519, July 18, 1944, now Patent No. 2,541,879,

dated February 13, 1951.

Divided and this application September 29, 1951, Serial No.

Claims.

My invention relates to alternating current railway track circuits, and more particularly to alternating current track circuits using vacuum tubes for track relays.

The present application is a division of my copending application, Serial No. 665,944, filed April 30, 1946, now Patent No. 2,591,456, which is a division of Letters Patent of the United States No. 2,541,879, granted February 13, 1951, for Vacuum Tube Circuits.

When a vacuum tube and particularly a gas tube is used as a relay for a railway track circuit, the bias voltage used to control the conductive condition of the tube must be checked because the loss of a bias voltage might result in the tube being made conductive corresponding to the unoccupied condition of the track circuit when the section is occupied.

Accordingly, a feature of my invention is the provision of track circuit apparatus incorporating novel and improved means to check the bias voltage of a gas tube used as a track relay and to assure proper phase relationship for the .voltages of the different tube circuits.

Other features, objects and advantages embodying my invention will appear as the specification progresses.

The foregoing features, objects and advantages embodying my invention are accomplished by a circuit arrangement which includes the shield grid or control electrode and the source of bias voltage in series in a bias circuit, and through which circuit power for the anode circuit is obtained. In this way a loss of the bias voltage or a broken element of the bias circuit results in a loss of power for the anode circuit and the tube cannot be fired in response to .such failure. The control grid circuit includes means through which the phase relationship of the voltage applied to the control grid from the track rails can be preselected and thus proper phase relationship between the voltage of the control grid circuit and the voltages of the anode and shield grid circuits can .be predetermined.

I shall describe .one form of alternating current track circuit apparatus embodying my inventioILand shall then point out the novel features thereof in claims.

Theaccompanying ,drawing is a diagrammatic view showing one form of railway track circuit embodying my invention when using a gas tube and an alternating current.

Referring to the drawing, the reference characters la and lb designate the track rails of a stretch of railway track formed by the usual insulated rail joints with a track section D-E, and which section may be one section of a series of sections of a signal system. Section DE is provided with a track circuit comprising a source of current connected across the rails at one end of the section and a track relay connected across the rails at the opposite end of the section. The immediate source of current for the track circuit of section D-E is a track transformer TE, a primary winding 6 of which is connected to an alternating current transmission line including line wires LI and L2 connected to a generator, not shown. A secondary winding 1 of transformer TE is connected across the rails la and lb a current limiting impedance 8 being preferably interposed in the connection.

The track relay for section D-E comprises a vacuum tube VI and associated circuits. Tube Vi may take different forms, and it is disclosed as an indirectly heated gas tetrode having an anode 9, a cathode lo, a control grid ll and a shield grid l2. Tube Vl is provided with two terminals for the shield grid l2, each end of the grid l2 being connected to a terminal. Thus, a circuit connected to the two terminals of the shield grid includes the shield grid in series so that any break in the shield grid or its connections within the tube will interrupt the circuit. The filament of the tube VI is heated from a secondary winding l3 of a line transformer TL, a primary winding 14 of which transformer is connected across the transmission line.

Tube Vl is provided with a control grid circuit receiving energy from the track rails through a track transformer TRD and a phase shifting impedance. Specifically, a primary winding 2 of transformer 'IRD is connected across the rails la and lb through wires 61 and 68, a resistor 69 being preferably connected in multiple with winding .2. Secondary winding 4 of transformer flRD is included in the control grid circuit which extends from grid ll through resistor IE to the junction terminal of an adjustable inductance l6 and a resistor 5 connected in series across the outside terminals of winding 4, and from an intermediate terminal of winding through a bias battery H and wire I0 to cathode l0. Thus, the current supplied to the rails through track transformer TE causes a voltage to be applied to the control grid ii of tube VII, the phase of the voltage applied to the grid with respect to the phase of the voltage across the rails being predetermined through the inductance i6 and resistor 5. The resistor 69 is provided in order to limit the amount of phase shift with changes in ballast conditions, but such resistor may not be needed. Also, the bias battery H is provided to give a normal negative bias voltage, but such bias battery may not be required.

Shield grid or control electrode 52 is included in a biasing circuit that can be traced from the right-hand terminal of secondary winding ii of line transformer TL through Wire'iii, primary winding IQ of a transformer'lfilwire 26, one terminal of the shield grid I2, the shield grid 12, the

' other terminal of the grid and wire 2| to the lefthand terminal of windin Ii. Wire is is connected to cathode it of the tube through wires 25-and H3, and thus the shield grid i2 is of a potential with respect to cathode l0 proportional to the voltage of secondary winding H. An anode circuit for tube VI extends from the top terminal of secondary winding 22 of transformer TP through a battery 12, resistor 23, winding of a relay CR, wire 2 3, plate 9 and intervening tube space to cathode id of tube V! and wires "53 and 25 to the other terminal of winding 22. It is to be seen that secondary winding ii of the line transformer TL not only supplies a bias voltage for the shield grid l2 with respect to cathode it but also supplies power through transformer T? to the anode circuit of the tube. Thus a loss of power at secondary winding ll or a broken circuit element for the biasing circuit of shield grid l2 will result in a loss of power for the anode circuit of the tube.

Plus and minus signs have been placed on certain of the circuit elements of the drawing to indicate the relative polarityof the parts during one half cycle of the voltage of the transmission line Ll--L2, the relative polarity of these circuit parts being reversed from that indicated during the other half cycle of the voltage. half cycle, the voltage is that indicated by the plus and minus signs, the shield grid i2 is negative in potentialwith respect to cathode it and the anode 9 is positive in potential with respect to the cathode. The parts are so proportioned that the higher voltages of such half cycle applied to the anode are sufficient to fire the tube, except for the negative bias effected through the shield grid i2. It is to be pointed out that battery i2 is of a voltage insufficient to fire tube V! and serves to aid in preselecting the portion of the cycle of the alternating voltage supplied through transformer TP and the tube is conductive. The battery i2 may not be needed and may be omitted.

Normally, that is, when the track section D-E is unoccupied, the control grid H is driven positive in potential with respect to cathode Ii! during the half cycle the anode 9 is positive and such positive voltage for the control grid i 1 causes tube V] to be fired and relay CR energized by the anode current. During the following half cycle of the voltage the anode 9 is negative with respect to the cathode l!) and the tube is deionized. On the next positive half cycle the tube is fired again so that relay CR is energized by impulses of During the d the anode current and its armature is retained picked up as long as such impulses of current flow because of the slow release characteristic of the relay. It is to be observed that the proper phase relationship of the voltage applied to the control grid H is preselected by the adjustment of the inductance l6 and resistor 5.

When the track section D-E is occupied, the control voltage impressed across control grid H and cathode it is shunted and the tube VI remains non-conductive because of the bias voltage applied to the shield grid l2.

It is apparent that there is disclosed in the drawing a track circuit usin a gas tube as a track relay and through which tube a control relay CR is retained energized in response to the track section being unoccupied and is deenergized when the section is occupied. Furthermore, a loss of power at winding ll of the line transformer so that there is a loss of bias voltage for the shield grid l2 results in a loss of power for the anode circuitand the tube cannot be fired because of such failure. Also, any broken circuit element for the shield grid circuit results in a loss of power forthe anode circuit and the tube cannot be fired because of such a broken circuit element.

It is to be understood that my invention is not limited to a shield grid as the control electrode of a tube, to be provided with two terminals and included in series with a bias voltage source, and other tube electrodes can be used.

Although I have herein shown and described but one form of alternating current railway track circuits embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In a railway track circuit, the combination comprising, a track section, a source of alternating current connected across the rails at the exit end of the section; a gas tube having an anode, a cathode, a control grid and a shield grid; a line transformer having a primary winding connected to said current source; another transformer, a shield grid circuit including in series a secondary winding of said line transformer, a primary winding of said other transformer and said shield grid; said cathode connected to said shield grid circuit at a point intermediate said secondary winding of the line transformer and said primary winding, of said another transformer to bias said shield grid with respect to the cathode, an anode circuit connected between said anode and cathode and including a secondary winding of said other transformer, said secondary winding poled for said shield grid to be negative in potential with respect to said cathode the half cycle of said alternating current source said anode is positive in potential with respect to said cathode to avoid firing said tube, means to connect said track rails across said control grid and cathode, said last mentioned means being poled for said track circuit current to drive said control grid positive in potential with respect to the cathode to fire the tube each half cycle said anode is positive, and control means connected to said anode circuit energized when said tube is conductive.

2, In a railway track circuit the combination comprising, a track section, a source of alternating current, means including a track transformer to connect said source across the rails adjacent one end of the section, a gas tube having an anode, a cathode and a first and a second control grid; said second control grid provided with two terminals one connected to each end of the grid to include the grid in series between the two terminals, a line transformer provided with a primary and a secondary winding and having its primary winding connected to said current source, another transformer provided with a primary and a secondary winding; a biasing circuit including in series said secondary winding of said line transformer, said primary winding of said another transformer and said second control grid with its two terminals; an anode circuit including said secondary winding of said another transformer, said anode and tube space to said cathode and a connection to said biasing circuit at a point intermediate the secondary winding of the line transformer and the primary winding of said another transformer, said biasing and anode circuits poled for said second grid to be negative in potential with respect to the cathode the half cycle of the alternating current said anode is positive in potential with respect to the cathode, circuit means including a phase shifting means to connect said first control grid and cathode across the rail adjacent the other end of said section, said circuit means poled for the voltage derived from said track transformer through the track section to render said first control grid positive in potential with respect to the cathode the half cycle of the alternating current said second control grid is negative in potential with respect to the cathode whereby the anode circuit is effective to fire the tube, and control means connected to said anode circuit energized by the current thus caused to now in the anode circuit when the tube is fired.

3, In a railway track circuit the combination comprising, a track section, a source of alternating current, means to connect said source across the rails at one end of said section; an electron tube having an anode, a cathode and a first and a second control grid; said second control grid provided with two terminals one connected to each end of the grid to include the grid in series between the two terminals, a line transformer provided with a primary and a secondary winding and having its primary winding connected to said source, another transformer provided with a primary and a secondary winding; a biasing circuit including in series said secondary winding of said line transformer, said primary winding of said another transformer and said second control grid with its two terminals; an anode circuit including said secondary winding of said another transformer, a control relay and said anode and tube space to said cathode, a point of said anode circuit intermediate the cathode and said secondary winding of said another transformer being connected to said biasing circuit at a point intermediate said secondary winding of the line transformer and said primary winding of the another transformer, said anode and biasing circuit poled for said second control grid to be negative in potential with respect to said cathode the half cycle of the alternating current said anode is positive in potential with respect to the cathode whereby said anode circuit is ineffective to render said tube conductive, circuit means including a phase shifting means to connect said first control grid and cathode across the rails at the other end of said section and poled for the voltage derived from said track rails due to the energy supply through the track transformer to render said first '6 grid positive in potential with respect to the oathode the half cycle the second grid is negative in potential with respect to the cathode, whereby said anode circuit is effective to render the tube conductive and energize said relay by the current thus caused to fiow in the anode circuit.

4, In a railway track circuit the combination comprising, a track section, a source of alterna ting current, means to couple said source across the rails at one end of said section to apply a voltage to the rails; a gas tube having an anode, a cathode and a first and a second control grid; said second grid provided with two terminals one connected to each end of the grid; energy transfer means including a first, second and a third winding, said first and said second windings being electrically connected, said first winding inductively coupled to said current source to receive a voltage, said second and said third windings being inductively coupled, a biasing circuit including in series said first and second windings and said second grid and its two terminals, said biasing circuit being energized by the voltage induced in said first winding, said cathode connected to said biasing circuit intermediate said first and second windings whereby the second grid has a given bias voltage with respect to said cathode due to the voltage drop in said second winding, an anode circuit including said third winding and connected across said anode and cathode, said third winding coupled to said second winding to inductively receive a voltage due to the biasing circuit current fiowing in said second winding, said voltage induced in said third winding having a magnitude effective to fire the tube but maintained ineffective to fire the tube due to said given bias voltage of the second grid with respect to said cathode, circuit means having a phase shifting means to connect said first control grid and cathode across the rails of said section to apply the voltage of the rails to the first grid, said circuit means being poled for the voltage thus applied to the first grid to counteract said bias voltage of said second grid and enable the voltage of said third winding to fire the tube, and a relay having a winding interposed in said anode circuit and energized by the current flowing in said anode circuit due to the firing of said tube.

5. In a railway track circuit, the combination comprising, a track section, a source of alternating current, means including a track transformer to connect said source across the rails at one end of said section; an electron tube having an anode, a cathode and a first and a second control grid; said second grid provided with two terminals one connected to each end of the grid, a line transformer provided with a primary and a secondary winding and having its primary winding connected to said current source; an auxiliary transformer having a first and a second winding; a biasing circuit including said secondary winding of the line transformer, said first winding of said auxiliary transformer, a first one of said terminals, said second grid and a second one of said terminals; said cathode connected to said biasing circuit at a selected terminal of said secondary winding of the line transformer whereby said second grid is biased with respect to the cathode due to the voltage of said secondary winding, an anode circuit connected across said anode and cathode and including said secondary winding of said auxiliary transformer and a control relay, the voltage induced in said secondary winding of said auxiliary transformer effective to cause conductive current to flow through said tube but maintained ineffective due to said bias voltage of said second grid, circuit means to connect said first grid and cathode across the rails of said section to apply to the first grid a voltage derived from said source through the rails of the section, said circuit means poled for said voltage applied to said. first grid to counteract said bias voltage of said second grid and render the voltage of said secondary winding of said auxiliary transformer efiective to cause current to flow through said tube and energize said relay.

' PAUL N. MARTIN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,919,064 Hull Jul 18, 1933 2,282,706 Chireux et a1 May 12, 1942 Ask w f M 

